Nutrient regulation of the saprotroph to parasite transition in Pochonia chlamydosporia a soil microbial inoculant for nematode control

植物寄生线虫以植物根系为食，阻碍它们的生长，使根系从土壤中吸收养分和水分的效率降低。尽管采取了控制措施，但受线虫感染的作物产量下降，全世界每年的损失估计高达1000亿美元。线虫显著降低了作物的水分利用效率，对撒哈拉以南非洲气候变化影响的预测表明，它们对作物的损害将显著增加。根结线虫（Meloidogyne spp.）是大多数热带作物的主要线虫害虫，可能导致非洲易感作物的作物全部歉收。在集约化种植系统中，种植者依靠植物抗性和化学品来管理线虫害虫。杀线虫剂是作物保护中使用的一些毒性最大的产品，由于环境问题和公众要求减少对农用化学品依赖的压力，一些欧洲国家已禁止使用杀线虫剂。迫切需要开发其他控制方法来取代现有的杀线虫剂。该提案建立在以下基础之上：1)洛桑研究所和古巴哈瓦那国家农业研究中心的合作研究，该研究已经开发出了一种居住在根际的真菌——衣孢Pochonia chlamydosporia，作为一种生物防治剂；2)先前由英国国际发展部资助的研究（作物保护计划项目R8296）对肯尼亚衣孢P. chlamydosporia的选择生物型进行了评估。该真菌在植物根系表面腐生生长，与Meloidogyne产的线虫虫卵接触后转变为寄生虫，破坏含有感染性幼虫的虫卵，从而产生下一代线虫；一种作物上可能有好几代，但单次施用真菌可显著减少线虫的侵扰。土壤中真菌的丰度与其寄生活性之间没有简单的关系，寄生活性受真菌营养状况的影响很大。有机土壤改良剂已被用于大大增加真菌在土壤中的丰度，但这种处理并不一定增加生物控制水平。我们将研究影响线虫卵真菌寄生率的营养因素。我们已经从衣孢单胞菌中鉴定、测序并克隆了VCP1基因，该基因编码一种碱性丝氨酸蛋白酶，参与感染过程的初始阶段，是真菌寄生阶段开始的一个指标。营养因子对该基因表达的影响将用于确定影响寄生期开始的因素，这对生物控制至关重要。这项关于真菌营养对生物防治活性影响的基础研究将得到内罗毕大学关于特定碳氮比及其提取物对真菌丰度和寄生活性影响的研究的补充。这一联系将为在典型的养分枯竭的土壤中研究当地的线虫侵扰和土壤改良剂类型提供机会。大学的同事们拥有进行研究的设施和专业知识，并对在洛桑进行的实验提出修改建议。洛桑研究所和内罗毕大学的两个研究小组都是东非和南部非洲线虫学倡议（NIESA）的一部分，该倡议由盖茨比慈善基金会支持，该基金会将英国和肯尼亚、马拉维、坦桑尼亚、乌干达和津巴布韦的线虫学家聚集在一起，NIESA形成了一个与当地种植者和企业家密切联系的网络，并将确保项目产出的既定吸收途径。

Plant parasitic nematodes feed on plant roots, stunt their growth and make root systems less efficient at withdrawing nutrients and water from soil. Yields of nematode-infected crops are reduced and annual losses worldwide are estimated to cost US$100b, despite control measures. Nematodes significantly reduce the water use efficiency of crops and climate change impacts predicted for sub-Saharan Africa suggest that their damage to crops will significantly increase. Root-knot nematodes (Meloidogyne spp.) are the major nematode pests of most tropical crops and may cause total crop failures on susceptible crops in Africa. In intensive cropping systems growers depend on plant resistance and chemicals to manage nematode pests. Nematicides are some of the most toxic products used in crop protection and their use has been banned in several European countries due to environmental concerns and public pressures to reduce dependence on agro-chemicals. There is an urgent need to develop other control methods to replace current nematicides. This proposal builds on a) collaborative research at Rothamsted and the Centro Nacional de Sanidad Agropecuaria, Havana, Cuba, which has led to the development of a rhizosphere-inhabiting fungus, Pochonia chlamydosporia, as a biological control agent and b) selected biotypes of P. chlamydosporia from Kenya evaluated in previous DFID funded research (Crop Protection Programme Project R8296). The fungus grows saprotrophically on the surface of plant roots and switches to become a parasite on contact with nematode eggmasses produced by Meloidogyne spp. It destroys the eggs that contain the infective juveniles, which give rise to the next nematode generation; there may be several generations on a crop but single applications of the fungus significantly reduce nematode infestations. There is no simple relationship between the abundance of the fungus in soil and its parasitic activity, which is much affected by the nutritional status of the fungus. Organic soil amendments have been used to greatly increase the abundance of the fungus in soil but such treatments do not necessarily increase the levels of biological control. We will study the nutritional factors that affect the rates of fungal parasitism of nematode eggs. We have identified, sequenced and cloned the VCP1 gene from P. chlamydosporia, which encodes an alkaline serine proteinase involved in the initial stages of the infection process and is an indicator of the beginning of the parasitic phase in the fungus. The influence of nutritional factors on the expression of this gene will be used to identify factors that affect the onset of the parasitic phase, essential for biological control. This basic research on the effects of fungal nutrition on biological control activity will be complemented by studies at the University of Nairobi on the effects on fungal abundance and parasitic activity of selected soil amendments with defined carbon:nitrogen ratios and their extracts. The link will provide opportunities to work with local nematode infestations and types of soil amendments in typical nutrient-depleted soils. Colleagues in the University have the facilities and expertise to conduct the research and to suggest modifications to the experimentation conducted at Rothamsted. Both the research groups at Rothamsted and the University of Nairobi are part of the Nematology Initiative in East and Southern Africa (NIESA), supported by the Gatsby Charitable Foundation, which brings together nematologists within the UK and in Kenya, Malawi, Tanzania, Uganda and Zimbabwe, NIESA forms a network with close links to local growers and entrepreneurs and will ensure an established uptake pathway for the outputs of the project.